GB2094346A - Aluminium cells - Google Patents

Abstract

In an electric cell for the manufacture of aluminium, the cell having a carbon floor and carbon walls 14 constituted by a plurality of abutting carbon or graphite blocks, at least some of the blocks are connected together by heat pipes 26, so that variations in temperature of the carbon or graphite blocks constituting the walls of the cell can be quickly evened out. Each heat pipe is a sealed, low pressure, boiling/condensing tubular unit utilising capillary action for condensate return to an evaporator (heat input) section from a condenser (heat removal section). The heat pipes are preferably connected in position with a suitable paste. <IMAGE>

Description

SPECIFICATION Aluminium cells The invention relates to aluminium manufacture and has for its object to provide an improvement therein.

Aluminium is generally made in a so-called electric cell having a horizontal carbon or graphite floor lining constituting a cathode, carbon anodes extending vertically downwards towards the cathode, and carbon or graphite lined side walls.

In use of the cell, alumina is decomposed and dissolved in a quantity of molten cryolite by a very large electric current and the cell operates at a very high temperature.

An important requirement in the operation of an aluminium cell is to be able to freeze a layer of flux "cryolite" onto the side walls to protect the carbon or graphite lining of the walls. It has previously been proposed to make the lining of the side walls of high thermal conductivity carbon blocks so that this can be achieved but these have the disadvantage of being of low electrical resistivity so that the required flow of high electrical energy from the carbon anodes to the floor of the cell is affected, that is to say is deflected towards the side walls. The invention has for its object to facilitate the required freezing of the flux cryolite onto the side walls in a very simple manner.

According to the invention, there is provided an electrical cell for the manufacture of aluminium, the cell having a carbon floor and carbon walls constituted by a plurality of abutting carbon or graphite blocks at least some of said blocks constituting the walls being connected together by means of heat pipes (that is to say low pressure boiling/condensing units) so that variations in temperature of said blocks in different parts of the cell walls will quickly be evened out. The heat pipes which connect adjacent carbon or graphite blocks will preferably be connected in position with a suitable paste.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which: Fig. 1 is a diagrammatic view of an electric cell for the production of aluminium, Fig. 2 is a sectional view through a part of the carbon or graphite walls of the aluminium cell, and Fig. 3 is a diagrammatic illustration of a socalled heat pipe.

Referring now to Fig. 1, the electric cell there illustrated for the production of aluminium includes an outer casing consisting of a steel box 10 with a base of insulating brick 1 2 and carbon side walls 14 forming a container and support.

Inside the lined casing, carbon blocks are cemented together with a suitable paste to form the floor 1 6 of a shallow bath, the floor blocks constituting a cathode when the cell is in operation. The blocks forming the floor are laid on alumina powder or other insulating material 18 and the space between the floor blocks and the carbon side walls is filled with ramming material 20.

An anode construction generally indicated 22 is shown to be constituted by a plurality of pre baked carbon blocks 24 (only two of which are shown in the drawing) extending vertically downwards from a carrier (not shown). When the cell is in use, an electrolyte consisting largely of molten cryolite will be contained in the shallow bath formed by the carbon blocks 14 and a large electric current will be passed from the anode to the cathode. The cell will operate at a temperature in the region of 1 0000C.

During the operation of the cell it is important that all the carbon blocks forming the side walls of the bath containing electrolyte should all be at substantially the same temperature so that the requirement for the freezing of a layer of flux "cryoiite" onto the side walls to protect the carbon side walls is facilitated. Consequently, as shown in Fig. 2, adjacent blocks constituting the side walls 14 are connected together by means of so-called heat pipes generally indicated 26 so that any variations in temperature of said blocks in different parts of the cell walls will quickly be evened out.

Each heat pipe is a sealed, low pressure, boiling/condensing tubular unit utilising capillary action for condensate return to an evaporator (heat input) section from a condenser (heat removal) section. Such units are commerciaily available. A heat pipe is illustrated diagrammatically in Fig. 3 and is shown to include a hollow tube 28 with closed ends and a lining material constituting a wick 30. The tube has been evacuated of air and a quantity of a suitable working fluid has been introduced into the tube before it has been sealed.

The arrangement is such that throughout the operation of the cell any concentrations of heat are quickly dispersed by the heat pipes so that optimum efficiency of production can be maintained. It will of course be understood that the number of heat pipes required to ensure the free flow of heat can be determined by trial and experiment. For example, it may be found that more than one heat pipe extending between each pair of blocks, or selected blocks, would be desirable. The heat pipes require to be cemented in position with a suitable paste so that good thermal contact betwen the heat pipes and the carbon blocks is ensured.

1. An electric cell for the manufacture of aluminium, the cell having a carbon floor and carbon walls constituted by a plurality of abutting carbon or graphite blocks at least some of said blocks constituting the walls being connected together by means of heat pipes (that is to say low pressure boiling/condensing units) so that variations in temperature of said blocks in different parts of the cells walls will quickly be evened out.

2. An electric cell according to claim 1, in which

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Aluminium cells The invention relates to aluminium manufacture and has for its object to provide an improvement therein. Aluminium is generally made in a so-called electric cell having a horizontal carbon or graphite floor lining constituting a cathode, carbon anodes extending vertically downwards towards the cathode, and carbon or graphite lined side walls. In use of the cell, alumina is decomposed and dissolved in a quantity of molten cryolite by a very large electric current and the cell operates at a very high temperature. An important requirement in the operation of an aluminium cell is to be able to freeze a layer of flux "cryolite" onto the side walls to protect the carbon or graphite lining of the walls. It has previously been proposed to make the lining of the side walls of high thermal conductivity carbon blocks so that this can be achieved but these have the disadvantage of being of low electrical resistivity so that the required flow of high electrical energy from the carbon anodes to the floor of the cell is affected, that is to say is deflected towards the side walls. The invention has for its object to facilitate the required freezing of the flux cryolite onto the side walls in a very simple manner. According to the invention, there is provided an electrical cell for the manufacture of aluminium, the cell having a carbon floor and carbon walls constituted by a plurality of abutting carbon or graphite blocks at least some of said blocks constituting the walls being connected together by means of heat pipes (that is to say low pressure boiling/condensing units) so that variations in temperature of said blocks in different parts of the cell walls will quickly be evened out. The heat pipes which connect adjacent carbon or graphite blocks will preferably be connected in position with a suitable paste. In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which: Fig. 1 is a diagrammatic view of an electric cell for the production of aluminium, Fig. 2 is a sectional view through a part of the carbon or graphite walls of the aluminium cell, and Fig. 3 is a diagrammatic illustration of a socalled heat pipe. Referring now to Fig. 1, the electric cell there illustrated for the production of aluminium includes an outer casing consisting of a steel box 10 with a base of insulating brick 1 2 and carbon side walls 14 forming a container and support. Inside the lined casing, carbon blocks are cemented together with a suitable paste to form the floor 1 6 of a shallow bath, the floor blocks constituting a cathode when the cell is in operation. The blocks forming the floor are laid on alumina powder or other insulating material 18 and the space between the floor blocks and the carbon side walls is filled with ramming material 20. An anode construction generally indicated 22 is shown to be constituted by a plurality of pre baked carbon blocks 24 (only two of which are shown in the drawing) extending vertically downwards from a carrier (not shown). When the cell is in use, an electrolyte consisting largely of molten cryolite will be contained in the shallow bath formed by the carbon blocks 14 and a large electric current will be passed from the anode to the cathode. The cell will operate at a temperature in the region of 1 0000C. During the operation of the cell it is important that all the carbon blocks forming the side walls of the bath containing electrolyte should all be at substantially the same temperature so that the requirement for the freezing of a layer of flux "cryoiite" onto the side walls to protect the carbon side walls is facilitated. Consequently, as shown in Fig. 2, adjacent blocks constituting the side walls 14 are connected together by means of so-called heat pipes generally indicated 26 so that any variations in temperature of said blocks in different parts of the cell walls will quickly be evened out. Each heat pipe is a sealed, low pressure, boiling/condensing tubular unit utilising capillary action for condensate return to an evaporator (heat input) section from a condenser (heat removal) section. Such units are commerciaily available. A heat pipe is illustrated diagrammatically in Fig. 3 and is shown to include a hollow tube 28 with closed ends and a lining material constituting a wick 30. The tube has been evacuated of air and a quantity of a suitable working fluid has been introduced into the tube before it has been sealed. The arrangement is such that throughout the operation of the cell any concentrations of heat are quickly dispersed by the heat pipes so that optimum efficiency of production can be maintained. It will of course be understood that the number of heat pipes required to ensure the free flow of heat can be determined by trial and experiment. For example, it may be found that more than one heat pipe extending between each pair of blocks, or selected blocks, would be desirable. The heat pipes require to be cemented in position with a suitable paste so that good thermal contact betwen the heat pipes and the carbon blocks is ensured. CLAIMS

1. An electric cell for the manufacture of aluminium, the cell having a carbon floor and carbon walls constituted by a plurality of abutting carbon or graphite blocks at least some of said blocks constituting the walls being connected together by means of heat pipes (that is to say low pressure boiling/condensing units) so that variations in temperature of said blocks in different parts of the cells walls will quickly be evened out.

2. An electric cell according to claim 1, in which the heat pipes which connect adjacent carbon or graphite blocks are connected in position with a suitable paste.

3. An electric cell for the manufacture of aluminium, the cell being constructed, arranged and adapted to be used substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.